Re: [PATCH] docs/system/s390x: Add a chapter about s390x boot devices

[Cornelia Huck]

On Thu,  6 Aug 2020 17:05:07 +0200
Thomas Huth <thuth@redhat.com> wrote:

> Booting on s390x is a little bit different compared to other architectures.
> Let's add some information for people who are not yet used to this.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  docs/system/s390x/bootdevices.rst | 82 +++++++++++++++++++++++++++++++
>  docs/system/target-s390x.rst      |  1 +
>  2 files changed, 83 insertions(+)
>  create mode 100644 docs/system/s390x/bootdevices.rst
> 
> diff --git a/docs/system/s390x/bootdevices.rst 
> b/docs/system/s390x/bootdevices.rst
> new file mode 100644
> index 0000000000..68f0ffd450
> --- /dev/null
> +++ b/docs/system/s390x/bootdevices.rst
> @@ -0,0 +1,82 @@
> +Boot devices on s390x
> +=====================
> +
> +Booting with bootindex parameter
> +--------------------------------
> +
> +For classical mainframe guests (i.e. LPAR or z/VM installations), you always
> +have to exactly specify the disk where you want to boot from (or "IPL" from,

s/exactly/explictly/ ?

> +in s390x-speak -- IPL means "Initial Program Load"). Especially, there can

s/Especially/In particular/ ?

> +also be only one boot device according to the architecture specification, 
> thus
> +specifying multiple boot devices is not possible (yet).
> +
> +So for booting an s390x guest in QEMU, you should always mark the
> +device where you want to boot from with the ``bootindex`` property, for
> +example::
> +
> + qemu-system-s390x -drive if=none,id=dr1,file=guest.qcow2 \
> +                   -device virtio-blk,drive=dr1,bootindex=1
> +
> +For booting from a CD-ROM ISO image (which needs to include El-Torito boot
> +informatin for being bootable), it is recommended to specify a ``scsi-cd``

s/informatin for being/information in order to be/

> +device, for example like this::
> +
> + qemu-system-s390x -blockdev file,node-name=c1,filename=... \
> +                   -device virtio-scsi \
> +                   -device scsi-cd,drive=c1,bootindex=1
> +
> +Note that you really have to use the ``bootindex`` property to select the
> +boot device. The old-fashioned ``-boot order=...`` command of QEMU (and
> +also ``-boot once=...``) is not supported on s390x.

(...)

This looks good to me, and is certainly helpful. I can fix the nits
myself and apply it.

There's also some documentation regarding DASD IPL in the devel guide;
but as that is mostly helpful for people actually working with the
code, I don't think that it makes sense to cross-reference it.